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Auto merge of #4259 - Darth-Revan:origin/inherent_to_string, r=flip1995
Implement lint for inherent to_string() method. Fixes #4247 changelog: Implement two new lints: `inherent_to_string` and `inherent_to_string_shadow_display` 1) Emits a warning if a type implements an inherent method `to_string(&self) -> String` 2) Emits an error if a type implements an inherent method `to_string(&self) -> String` and also implements the `Display` trait
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,154 @@ | ||
| use if_chain::if_chain; | ||
| use rustc::hir::{ImplItem, ImplItemKind}; | ||
| use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass}; | ||
| use rustc::{declare_lint_pass, declare_tool_lint}; | ||
|
|
||
| use crate::utils::{ | ||
| get_trait_def_id, implements_trait, in_macro_or_desugar, match_type, paths, return_ty, span_help_and_lint, | ||
| trait_ref_of_method, walk_ptrs_ty, | ||
| }; | ||
|
|
||
| declare_clippy_lint! { | ||
| /// **What id does:** Checks for the definition of inherent methods with a signature of `to_string(&self) -> String`. | ||
| /// | ||
| /// **Why is this bad?** This method is also implicitly defined if a type implements the `Display` trait. As the functionality of `Display` is much more versatile, it should be preferred. | ||
| /// | ||
| /// **Known problems:** None | ||
| /// | ||
| /// ** Example:** | ||
| /// | ||
| /// ```rust | ||
| /// // Bad | ||
| /// pub struct A; | ||
| /// | ||
| /// impl A { | ||
| /// pub fn to_string(&self) -> String { | ||
| /// "I am A".to_string() | ||
| /// } | ||
| /// } | ||
| /// ``` | ||
| /// | ||
| /// ```rust | ||
| /// // Good | ||
| /// use std::fmt; | ||
| /// | ||
| /// pub struct A; | ||
| /// | ||
| /// impl fmt::Display for A { | ||
| /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { | ||
| /// write!(f, "I am A") | ||
| /// } | ||
| /// } | ||
| /// ``` | ||
| pub INHERENT_TO_STRING, | ||
| style, | ||
| "type implements inherent method `to_string()`, but should instead implement the `Display` trait" | ||
| } | ||
|
|
||
| declare_clippy_lint! { | ||
| /// **What id does:** Checks for the definition of inherent methods with a signature of `to_string(&self) -> String` and if the type implementing this method also implements the `Display` trait. | ||
| /// | ||
| /// **Why is this bad?** This method is also implicitly defined if a type implements the `Display` trait. The less versatile inherent method will then shadow the implementation introduced by `Display`. | ||
| /// | ||
| /// **Known problems:** None | ||
| /// | ||
| /// ** Example:** | ||
| /// | ||
| /// ```rust | ||
| /// // Bad | ||
| /// use std::fmt; | ||
| /// | ||
| /// pub struct A; | ||
| /// | ||
| /// impl A { | ||
| /// pub fn to_string(&self) -> String { | ||
| /// "I am A".to_string() | ||
| /// } | ||
| /// } | ||
| /// | ||
| /// impl fmt::Display for A { | ||
| /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { | ||
| /// write!(f, "I am A, too") | ||
| /// } | ||
| /// } | ||
| /// ``` | ||
| /// | ||
| /// ```rust | ||
| /// // Good | ||
| /// use std::fmt; | ||
| /// | ||
| /// pub struct A; | ||
| /// | ||
| /// impl fmt::Display for A { | ||
| /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { | ||
| /// write!(f, "I am A") | ||
| /// } | ||
| /// } | ||
| /// ``` | ||
| pub INHERENT_TO_STRING_SHADOW_DISPLAY, | ||
| correctness, | ||
| "type implements inherent method `to_string()`, which gets shadowed by the implementation of the `Display` trait " | ||
| } | ||
|
|
||
| declare_lint_pass!(InherentToString => [INHERENT_TO_STRING, INHERENT_TO_STRING_SHADOW_DISPLAY]); | ||
|
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||
| impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InherentToString { | ||
| fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, impl_item: &'tcx ImplItem) { | ||
| if in_macro_or_desugar(impl_item.span) { | ||
| return; | ||
| } | ||
|
|
||
| if_chain! { | ||
| // Check if item is a method, called to_string and has a parameter 'self' | ||
| if let ImplItemKind::Method(ref signature, _) = impl_item.node; | ||
| if impl_item.ident.name.as_str() == "to_string"; | ||
| let decl = &signature.decl; | ||
| if decl.implicit_self.has_implicit_self(); | ||
|
|
||
| // Check if return type is String | ||
| if match_type(cx, return_ty(cx, impl_item.hir_id), &paths::STRING); | ||
|
|
||
| // Filters instances of to_string which are required by a trait | ||
| if trait_ref_of_method(cx, impl_item.hir_id).is_none(); | ||
|
|
||
| then { | ||
| show_lint(cx, impl_item); | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| fn show_lint(cx: &LateContext<'_, '_>, item: &ImplItem) { | ||
| let display_trait_id = | ||
| get_trait_def_id(cx, &["core", "fmt", "Display"]).expect("Failed to get trait ID of `Display`!"); | ||
|
|
||
| // Get the real type of 'self' | ||
| let fn_def_id = cx.tcx.hir().local_def_id(item.hir_id); | ||
| let self_type = cx.tcx.fn_sig(fn_def_id).input(0); | ||
| let self_type = walk_ptrs_ty(self_type.skip_binder()); | ||
|
|
||
| // Emit either a warning or an error | ||
| if implements_trait(cx, self_type, display_trait_id, &[]) { | ||
| span_help_and_lint( | ||
| cx, | ||
| INHERENT_TO_STRING_SHADOW_DISPLAY, | ||
| item.span, | ||
| &format!( | ||
| "type `{}` implements inherent method `to_string(&self) -> String` which shadows the implementation of `Display`", | ||
| self_type.to_string() | ||
| ), | ||
| &format!("remove the inherent method from type `{}`", self_type.to_string()) | ||
| ); | ||
| } else { | ||
| span_help_and_lint( | ||
| cx, | ||
| INHERENT_TO_STRING, | ||
| item.span, | ||
| &format!( | ||
| "implementation of inherent method `to_string(&self) -> String` for type `{}`", | ||
| self_type.to_string() | ||
| ), | ||
| &format!("implement trait `Display` for type `{}` instead", self_type.to_string()), | ||
| ); | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,84 @@ | ||
| #![warn(clippy::inherent_to_string)] | ||
| #![deny(clippy::inherent_to_string_shadow_display)] | ||
|
|
||
| use std::fmt; | ||
|
|
||
| trait FalsePositive { | ||
| fn to_string(&self) -> String; | ||
| } | ||
|
|
||
| struct A; | ||
| struct B; | ||
| struct C; | ||
| struct D; | ||
| struct E; | ||
|
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||
| impl A { | ||
| // Should be detected; emit warning | ||
| fn to_string(&self) -> String { | ||
| "A.to_string()".to_string() | ||
| } | ||
|
|
||
| // Should not be detected as it does not match the function signature | ||
| fn to_str(&self) -> String { | ||
| "A.to_str()".to_string() | ||
| } | ||
| } | ||
|
|
||
| // Should not be detected as it is a free function | ||
| fn to_string() -> String { | ||
| "free to_string()".to_string() | ||
| } | ||
|
|
||
| impl B { | ||
| // Should not be detected, wrong return type | ||
| fn to_string(&self) -> i32 { | ||
| 42 | ||
| } | ||
| } | ||
|
|
||
| impl C { | ||
| // Should be detected and emit error as C also implements Display | ||
| fn to_string(&self) -> String { | ||
| "C.to_string()".to_string() | ||
| } | ||
| } | ||
|
|
||
| impl fmt::Display for C { | ||
| fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { | ||
| write!(f, "impl Display for C") | ||
| } | ||
| } | ||
|
|
||
| impl FalsePositive for D { | ||
| // Should not be detected, as it is a trait function | ||
| fn to_string(&self) -> String { | ||
| "impl FalsePositive for D".to_string() | ||
| } | ||
| } | ||
|
|
||
| impl E { | ||
| // Should not be detected, as it is not bound to an instance | ||
| fn to_string() -> String { | ||
| "E::to_string()".to_string() | ||
| } | ||
| } | ||
|
|
||
| fn main() { | ||
| let a = A; | ||
| a.to_string(); | ||
| a.to_str(); | ||
|
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| to_string(); | ||
|
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| let b = B; | ||
| b.to_string(); | ||
|
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| let c = C; | ||
| C.to_string(); | ||
|
|
||
| let d = D; | ||
| d.to_string(); | ||
|
|
||
| E::to_string(); | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,28 @@ | ||
| error: implementation of inherent method `to_string(&self) -> String` for type `A` | ||
| --> $DIR/inherent_to_string.rs:18:5 | ||
| | | ||
| LL | / fn to_string(&self) -> String { | ||
| LL | | "A.to_string()".to_string() | ||
| LL | | } | ||
| | |_____^ | ||
| | | ||
| = note: `-D clippy::inherent-to-string` implied by `-D warnings` | ||
| = help: implement trait `Display` for type `A` instead | ||
|
|
||
| error: type `C` implements inherent method `to_string(&self) -> String` which shadows the implementation of `Display` | ||
| --> $DIR/inherent_to_string.rs:42:5 | ||
| | | ||
| LL | / fn to_string(&self) -> String { | ||
| LL | | "C.to_string()".to_string() | ||
| LL | | } | ||
| | |_____^ | ||
| | | ||
| note: lint level defined here | ||
| --> $DIR/inherent_to_string.rs:2:9 | ||
| | | ||
| LL | #![deny(clippy::inherent_to_string_shadow_display)] | ||
| | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | ||
| = help: remove the inherent method from type `C` | ||
|
|
||
| error: aborting due to 2 previous errors | ||
|
|